Google has introduced 2-factor authentication by using FIDO U2F Security Key (Fast IDentity Online).
The users have to purchase themselves the USB FIDO U2F Ready hardware,there are different price ranges from 6 Euros and up.
The Fido U2F token is only supported and available currently on Google Chrome browser version 38 or newer on the desktop or in Chrome OS. Users of Internet Explorer, Safari, Firefox, etc. or mobile devices can not benefit from the new technology.